Do you keep a log? Keeping track of what he's eating might help narrow down the problem food. Is he having trouble with bowel movements as well? A few of the more common constipating foods I can think of are bananas and rice cereal. Toast is an issue too but I'm assuming since he's wheat intolerant he is not eating any. Not sure about sweet potato, but the simplest thing to do would be to stop giving it for awhile and see if there is improvement, then try reintroducing it and looking for signs that it's a problem. As far as windy foods, a few I can think of are brocoli, garlic, onions, cabbage, cauliflower too I think. What does he eat at the moment, maybe we can see something that stands out.